Back in my younger days I worked with a local council roads department, that meant blocked sewers etc. etc, usually outside a hotel you would have this problem, and this was over 40yrs ago, without the tech gear they will have now, or the chemicals, we had to push metal rods up the pipe with large cork screw type attachment, work it into the fat and draw it back to the manhole, it was the most disgusting stink ever, being sticky and clingy, it stuck to everything, just thinking about it now makes me want to throw up, yet we used to stop for lunch and eat without think about it, back then. Jim